1. Field of the Invention
The invention relates to a power storage system of a hybrid vehicle including a motor driven with electric power supplied from a battery, and an engine, wherein the battery can be charged with electric power supplied from an external power supply.
2. Description of Related Art
A hybrid vehicle includes a motor and an engine as driving sources for running the vehicle. The hybrid vehicle is able to run using one or both of the engine and the motor, as the driving source(s).
In recent years, plug-in hybrid vehicles appeared, in which a battery that supplies electric power to a motor can be charged with electric power supplied from an external power supply. In a plug-in hybrid vehicle as described in Japanese Patent Application Publication No. 2013-119349 (JP 2013-119349 A), when the vehicle runs after completion of charging using the external power supply, vehicle control is performed in a running mode (CD mode) in which electric power stored in the battery is positively used until the state of charge (SOC) of the battery is reduced to a given value, while curbing or reducing the frequency of driving the vehicle, thus assuring improved fuel efficiency. To improve the fuel efficiency, it is necessary to curb or reduce the frequency of driving the engine while the vehicle is running in the CD mode.
In a system as described in Japanese Patent Application Publication No. 2008-126970 (JP 2008-126970 A), the engine is heated during external charging so that the temperature of the engine (the temperature of the engine coolant) is increased. With the engine thus heated in advance during external charging, the engine is less likely or unlikely to be driven for warm-up during vehicle running.
In a vehicle control system as described in Japanese Patent Application Publication No. 2011-259672 (JP 2011-259672 A), the battery is heated during external charging so that the temperature of the battery is increased. The output characteristics of the battery depend on the temperature, and the output of the battery is reduced if the temperature of the battery is lower than an appropriate temperature range. If the output of the battery is reduced, the engine is more likely to be driven so as to make up for the required output of the vehicle, for example. Therefore, the temperature of the battery is raised to the appropriate temperature range during external charging, so that the output of the battery is less likely or unlikely to be reduced, and the frequency of driving the engine is curbed or reduced.
Thus, in order to improve the fuel efficiency through running control in the CD mode after completion of charging using the external power supply, it is necessary to curb or reduce the frequency of driving the engine, by warming the engine and the battery through temperature control during external charging.